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What is a Sovtek 6H30,6C45, and 6C33CB?

In short, they are vacuum tubes. There are four stages to a tube amplifier. They are: the voltage amplifier stage, the phase splitter/invertor stage, the driver stage, and the power stage. Without getting into too much gory detail, the 6H30 and 6C45 tubes are amazingly linear. For this amplifier, this completely eliminates the need for corrective circuitry. The result sound is accurate, simple, and pure. The power stage requires a different type of tube, one which can handle a lot of power. The 6C33CB is a relic from the US/Soviet cold war era that is still in production. While the US was designing their military toys with transistors, Russia could not obtain that technology. As such, they continued their research and development into vacuum tubes. What resulted are some tubes with absolutely astounding features. The 6C33CB is one of those tubes. Originally designed as a voltage controller for MIG fighter microwave circuits, this tube can withstand multiple impact loads up to 3.5g and single impact loads up to 10g. On the flip side, the 6C33CB is a nightmare to drive because of its dynamic variations in impedance and response characteristics. We proudly admit that the proof of concept amplifier handles the 6C33CB most admirably. Actually, the dynamics of the amplifier extend from 10 Hz to over 200,000 Hz.

What are Class A and Push-Pull?

Class A and Push-Pull describe the architecture of the amplifier. A class A amplifier is the least efficient amplifier because the electronics are always working their little hearts out; however, it produces one of the least distorted most true sounds available. Push-Pull amplifiers use two tubes working together to get more power and to cancel out certain aspects of noise that can be created by the electronics.

Why tubes? Why Transistors?

These questions are enough to make the hair stand up on the back of any audiophile's neck! It is a debate that continues on with a theological zeal. Technically, there are only two ways to amplify signals. Their voltage swing can be increased, or their current swing can be increased. There is a mechanical analogy. When you run water through the kitchen sink and shut it off quickly, the pipes bang with the inertia of the water passing through them. The force of the water is dramatically changed through this process. This is much like current flowing through a wire. Voltage swing is like having the same water in the pipe, but having a balloon at one end and a piston at the other. Very little movement of the water will make large size changes in the balloon. Tubes work like the piston and the balloon. Transistors work like the kitchen sink. In truth, each has their strengths and weaknesses. We opted for tubes because, in general, there are fewer components required to make a tube amplifier work well. As such, the possibility of the sound being altered by a component is reduced. This keeps us in line with our original goals of simplicity and purity of sound.

What is Negative Feedback?

Negative feeback is a method of circulating a small piece of the output signal back through the circuitry to gain better control of the natural hysteresis of the output transformer. Negative feedback can also be used to flatten the frequency response of a given circuit.
 The reality is that it can slow the response of the amplifier and dull the sound of the finished product.

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